K2-7 b

Astrophysical Synthesis & Habitability Characterization

K2-7 b is a confirmed sub-neptune exoplanet orbiting the star K2-7, located approximately 2408.8 light-years (738.55 parsecs) from the Solar System. First announced in 2015 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0582% across the stellar disk), this world measures 4.035 Earth radii (0.36 Jupiter radii) and has a measured mass of 15.3 Earth masses. Combining its mass and radius yields a mean bulk density of 1.28 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.94 g⊕ (9.22 m/s²), and an escape velocity of 21.8 km/s.

In its orbital architecture around K2-7, K2-7 b completes one full revolution every 28.678 Earth days at a semi-major axis of 0.1867 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 70.8 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.24 carries the world between 0.1419 AU at periapsis and 0.2315 AU at apoapsis, driving measurable seasonal insolation cycles.

⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 786 K (+513°C / +955°F) and receiving 125.00 S⊕ (~170,125 W/m²), K2-7 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.

The host star K2-7 is classified as a stellar host with an effective photospheric temperature of 5,700 K, a radius of 1.533 R☉, a mass of 1.056 M☉, an estimated bolometric luminosity of 2.226 L☉. Stellar evolution modeling indicates an estimated stellar age of 8.6 Gyr and a metallicity of [Fe/H] = 0.049 dex (near-solar heavy-element abundance). From Earth, K2-7 shines at apparent V-band magnitude 13.453 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere.

Discovery Facility: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).